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In molecular biology, enzymes containing the cyclodeaminase domain function in channeling one-carbon units to the folate pool. In most cases, this domain acts as a formimidoyltetrahydrofolate cyclodeaminase, which catalyses the cyclisation of formimidoyltetrahydrofolate to methenyltetrahydrofolate as shown in reaction (1). In the methylotrophic bacterium ''Methylobacterium extorquens'', however, it acts as a methenyltetrahydrofolate cyclohydrolase, which catalyses the interconversion of formyltetrahydrofolate and methylenetetrahydrofolate, as shown in reaction (2). (1) 5-formimidoyltetrahydrofolate = 5,10-methenyltetrahydrofolate + NH(3) (2) 10- formyltetrahydrofolate = 5,10-methenyltetrahydrofolate + H(2)O In prokaryotes, this domain mostly occurs on its own, while in eukaryotes it is fused to a glutamate formiminotransferase domain (which catalyses the previous step in the pathway) to form the bifunctional enzyme formiminotransferase cyclodeaminase. The eukaryotic enzyme is a circular tetramer of homodimers, while the prokaryotic enzyme is a dimer.〔 The crystal structure of the cyclodeaminase enzyme from ''Thermaotogoa maritima'' has been studied.〔 It is a homodimer, where each monomer is composed of six alpha helices arranged in an up and down helical bundle, forming a novel fold. The location of the active site is not known, but sequence alignments revealed two clusters of conserved residues located in a deep pocket within the dimmer interface. This pocket was large enough to accommodate the reaction product and it was postulated that this is the active site. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cyclodeaminase domain」の詳細全文を読む スポンサード リンク
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